fix(pm): include resolved markets in Polymarket vol24h + remove Manifold from hub

[Flotapponnier]

Summary

• Polymarket vol24h fix: adds a second pagination pass for closed=true&active=false&end_date_min=<25h_ago> markets. Markets that resolved during the day are excluded from the active=true pass but still carry volume24hr > 0 from trades before resolution. The second pass (capped at 10 pages) captures their contribution and stops early when all rows show zero volume.
• Manifold removed from hub leaderboard: Manifold is play-money (mana), not a real-money venue. Removing from PM_VENUES stops it from appearing in the cross-venue table and from inflating the "Total volume 30d" and "Active markets" summary cards. The harness continues collecting Manifold data; only the hub display changes.

Test plan

• Deploy to staging and confirm the /prediction-markets hub no longer shows a Manifold row
• Check VPS logs after rebuilding ocb-pm-cohort-stats — look for [polymarket][polymarket] closed page=0 log line confirming the second pass runs
• Verify vol24h increases compared to previous tick (should be materially higher once closed markets are included)